The Design and SAR Analysis of Wearable UWB Antenna for Radiative Near-Field Wireless Power Transfer

This paper presents design of a wearable UWB (ultra-wide band) antenna and its corresponding SAR (specific absorption rate) analysis and power transfer capability estimation when it is placed on a human body. In this work, Polyimide with a thickness of 0.1 mm is used as the substrate material, and gold with a thickness of 200 nm is used for the patch and ground material. The dielectric constant and tangent loss of the polyimide substrate are 3.5 and 0.0002, respectively. The dimensions of the proposed antenna are
$30\times 30\times 0.1004\ \text{mm}^{3}$
. The designed antenna has the resonating frequency at 3.11 GHz and a bandwidth of 3.06GHz. The near-field gain of the designed antenna is 6.43 dBi. The SAR analysis generated SAR values of 0.138 W/kg and 0.147 W/kg for antenna placed on flat body model and curved body model, respectively, which are within the safe limit of 2 W/kg averaged over 10g of tissue as specified by the ICNIRP (International Commission of Non-Ionization Radiation Protection). This indicates that the antenna is safe and suitable for use in wireless wearable sensors.